Bathtub Brooder + Cleaning Question

Hello! My chicks are coming in very soon, which is exciting, and I'm setting up the brooder, I just have a few questions...as I've never used an unused bathtub before. lol What would be safe to line it with? Would garbage bags be OK, or would they potentially be able to ingest some if they scratched enough? Or would it be better to just do a layer of pine shavings over the tub floor?

One more question - is it OK to use a bit of plant based cleaner in the tub? I accidentally went ahead and did it since the tub was kind of gross and now I'm worried it will hurt them...I'm letting the room air out before I put any of the bags/bedding down but I just wanted to make sure. If is is bad, do I rinse out with vinegar to get rid of it or is there something else I can do?? I'm a little bit freaked out.